Abstract:

Oil wells are treated with latent acids containing a sulfonyl moiety,
wherein the latent acid is capable of providing an active acid after
injection into an oil well. The latent acids are converted to active
acids, such as mineral acids or strong organic acids, in the oil well,
with resultant dissolution of acid-soluble minerals that impede oil or
gas flow. RYSO2X is an exemplary latent acid, where: R is C(1)-C(30)
hydrocaryl alone, or appended to an oligomeric or polymeric chain, or
substituted; X is halogen; and Y is O, S, Se, or NR or a direct bond. M
is a Group IVA metal, a Group IVB metal, a Group IB metal, or a Group HB
metal. Other exemplary latent acids include amine functionality.

Claims:

1. A method of treating an oil well, comprising injecting into the well a
composition comprising a latent acid comprising a sulfonyl moiety,
wherein the latent acid is capable of providing an active acid after
injection into an oil well.

2. The method of claim 1, wherein the latent acid is a sulfonyl halide,
sulfonate ester, sulfonamide, or thiolsulfonate.

3. The method of claim 1, wherein the latent acid is a thiolsulfonate, the
method further comprising injecting into the well an oxidizing agent.

4. The method of claim 1, wherein the latent acid is an ester, amide, or
acid halide of methanesulfonic acid.

5. The method of claim 1, wherein the composition further comprises a
nucleophile.

6. The method of claim 1, wherein the step of injecting the composition
comprises injecting it into strata in the well having a temperature from
20 to 250.degree. C.

7. The method of claim 1, wherein the step of injecting the composition
comprises injecting it into strata in the well having a temperature from
50 to 150.degree. C.

8. The method of claim 1, wherein the latent acid is according to any of
formulas (I), (II), and (III)R1YSO2X
(I)R1YSO.sub.3.sup.-+NHR2R3R4
(II)(R1YSO3)p(OR2)q(NR3R4)rM
(III)wherein R1 is selected from the group consisting of
C1-C30 hydrocarbyl moieties, C1-C30 hydrocarbyl
moieties appended to an oligomeric or polymeric chain, and
C1-C30 hydrocarbyl moieties substituted with functional groups
containing halogen, oxygen, sulfur, selenium, silicon, tin, lead,
nitrogen, phosphorous, antimony, bismuth, aluminum, boron, or metals
selected from Groups IA-IIA and IB-VIIIB of the periodic table; X is a
halogen or ZCR2R3R4; Y and Z are independently O, S, Se,
or NR5, and Y may also be a direct bond; R2, R3, R4
and R5 are independently hydrogen or as defined for R1 and
wherein any two or more of R1, R2, R3, R4 and R5
may be interconnected to form one or more cyclic structures; M is a Group
IVA metal, a Group IVB metal, a Group IB metal, or a Group IIB metal; and
p+q+r=n wherein n is the valence of metal M.

9. The method of claim 8, wherein the step of injecting the composition
comprises injecting it into strata in the well containing predominately
silica-containing rock, and wherein the latent acid comprises
R1SO2F or R1YSO2F.

10. The method of claim 8, wherein the composition further comprises HCl
or HF.

11. The method of claim 8, wherein the step of injecting the composition
comprises injecting it into strata in the well containing predominately
silica-containing rock, wherein the latent acid comprises
R1SO2Cl or R1YSO2Cl, and wherein the composition
further comprises sodium fluoride, potassium fluoride, or barium
fluoride.

12. The method of claim 11, wherein the composition further comprises HCl
or HF.

13. The method of claim 8, wherein R1 is a C1-C30
hydrocarbyl moiety and each of R2, R3, R4 and R5 is
independently hydrogen or a C1-C30 hydrocarbyl moiety.

14. The method of claim 8, wherein R1 is a C1-C30
hydrocarbyl moiety substituted with a functional group containing
halogen, oxygen, sulfur, nitrogen, silicon, or phosphorus, and wherein
each of R2, R3, R4 and R5 is independently hydrogen
or a C1-C30 hydrocarbyl moiety substituted with a functional
group containing halogen, oxygen, sulfur, nitrogen, silicon, or
phosphorus.

15. The method of claim 8, wherein X is Cl.

16. The method of claim 8, wherein X is O-n-butyl or O-sec-butyl.

17. The method of claim 8, wherein X is O-n-octyl.

18. The method of claim 8, wherein X is O-2-ethylhexyl.

Description:

FIELD OF THE INVENTION

[0001]The invention relates to methods of treating oil or gas wells to
enhance flow rates of the oil or gas.

BACKGROUND OF THE INVENTION

[0002]Petroleum hydrocarbons are generically referred to as "oil" and
include both hydrocarbon gases and liquids. The proportion of gas to
liquids may vary and the commercial production may be predominately
gases, or hydrocarbon liquids, or both. Within the earth's crust,
reservoirs of such hydrocarbons typically occur within porous sedimentary
strata containing silica-based minerals (e.g., sandstone, feldspars)
and/or carbonate-based minerals (e.g., limestone, dolomite). Strata that
are largely carbonate will also contain silica-based minerals and vice
versa. Within these strata, the oil exists in microscopic pores
interconnected by networks of microscopic flow channels. Various gases,
water and brines also occupy the rock pores and are in contact with the
oil. In petroleum production, the hydrocarbons are accessed through a
wellbore drilled into the formation. The hydrocarbons flow through the
rock formation to the wellbore, and ultimately to the surface, if the
oil-bearing rock has pores of sufficient size and number to provide a
sufficiently unimpeded flow path. Unfortunately, the flow in many
formations is in fact somewhat impeded due to the presence of only
relatively few, and/or relatively small, pores.

[0003]In addition to poor flow of oil due to a naturally impermeable
formation, impeded flow can arise from "damage" to the formation. One
source of such damage sometimes occurs as a consequence of the well
drilling, completion, and production operations. This damage takes the
form of mineral particles from the drilling and completion fluids that
have coated the face of the wellbore or have invaded the near-wellbore
strata, and mineral particles originally from the oil-bearing strata that
were mobilized during the drilling, completion and production operations.
The damage from these particles may occur at or near the wellbore, but
may also occur anywhere along the flow path of the oil and water that
migrate through the formation.

[0004]One approach to dealing with flow-impeding particulate minerals is
called "matrix acidizing", which involves injecting an acid or acid-based
fluid, often along with other chemicals, through the wellbore to a
targeted strata such that the acid can (a.) react with and dissolve
particles and scale in the wellbore and near-wellbore strata or (b.)
react with and dissolve small portions of the strata to create alternate
flow paths around the damaged strata, thereby enhancing the permeability
of the rock. Hydrochloric and/or hydrofluoric acid are commonly used for
this purpose. A related process, called "acid fracturing", involves
injecting an acid and/or water, along with other chemicals, into the
wellbore under sufficient pressure to fracture the targeted strata and
create large flow channels through which the hydrocarbons can more
readily migrate to the wellbore.

[0005]One common problem with using these strong mineral acids as
acidizing agents is their poor radial penetration into the formation.
This is a consequence of their immediate reactivity with the first
damaging material or strata minerals with which they come into contact.
This typically occurs immediately at or near the wellbore or along
existing large fracture lines. This immediate reactivity may not be
desirable in some cases, particularly those in which the first contact is
likely to be in regions of the formation that have already been depleted
of their contained oil, and not in the smaller channels where significant
volumes of oil still reside.

SUMMARY OF THE INVENTION

[0006]The invention provides a method of treating an oil well that
includes injecting into the well a composition comprising a latent acid
comprising a sulfonyl moiety. The latent acid is capable of providing an
active acid after injection into an oil well.

DETAILED DESCRIPTION OF THE INVENTION

Latent Acids

[0007]This invention discloses a process for stimulating production of
hydrocarbons from a petroleum well by treatment with latent acids. As
used herein, the term "latent acid" means a compound that does not itself
have substantial acidic character, but which is capable of being
converted to a mineral acid or a strong organic acid ("active acid") that
is able to dissolve carbonates, silicates, sulfides, and/or other
acid-soluble materials in an oil well. As used herein, the term
"dissolve" includes reactive dissolution as well as simple dissolution.
The latent acids of this invention include all compounds containing a
sulfonyl moiety (--SO2--) capable of providing an active acid after
injection into an oil well. Three exemplary classes of such compound are
shown below, but the invention is not limited to these.

[0008]One class of latent acids of this invention consists of compounds
having structures according to formula (I).

R1YSO2X (I)

[0009]In formula (I), R1 is selected from C1-C30
hydrocarbyl moieties optionally appended to an oligomeric or polymeric
chain or substituted with functional groups containing halogen, oxygen,
sulfur, selenium, silicon, tin, lead, nitrogen, phosphorous, antimony,
bismuth, aluminum, boron, or metals selected from Groups IA-IIA and
IB-VIIIB of the periodic table; X is a halogen (F, Cl, Br, I) or
ZCR2R3R4; Y and Z are independently O, S, Se, or NR6,
and Y may also be a direct bond; and R2, R3, R4 and
R5 are independently hydrogen or as defined for R1. Hydrocarbyl
moieties for any of R1-R5 are typically any branched or linear
alkyl group, aralkyl group, alkaryl group, or cyclic or alicyclic group.

[0010]Suitable nonlimiting examples of groups suitable for use as any of
R1-R5 are include straight-chain or branched-chain alkyl groups
containing from one to six carbon atoms, such as methyl, ethyl, n-propyl,
isopropyl, n-butyl, 2-butyl, tert-butyl, isobutyl, n-pentyl, 2-pentyl,
tert-pentyl, isopentyl, neopentyl, 2-methylpentyl, n-hexyl, and isohexyl;
straight-chain or branched-chain alkyl groups containing from seven to
twenty carbon atoms, such as heptyl, 2-ethylhexyl, octyl, nonyl,
3,5-dimethyloctyl, 3,7-dimethyloctyl, decyl, undecyl, dodecyl, tridecyl,
tetradecyl, 3-methyl-10-ethyldodecyl, pentadecyl, hexadecyl, heptadecyl,
octadecyl, nonadecyl, eicosyl, and cocoalkyl; and hydrocarbyl groups
containing from 1 to about 14 carbon atoms such as cyclohexylmethyl,
benzyl, pinyl, pinylmethyl, phenethyl, p-methylbenzyl, phenyl, tolyl,
xylyl, naphthyl, ethylphenyl, methylnaphthyl, dimethylnaphthyl,
norbornyl, and norbornylmethyl. Further, any two or more of R1,
R2, R3, R4 and R5 may optionally be interconnected to
form one or more cyclic structures. Typically, if substituent groups are
incorporated in any of R1, R2, R3, R4 and R5,
the groups will contain halogen, oxygen, sulfur, nitrogen, silicon, or
phosphorus. The preparation of latent acids of formula (I) may be
effected by any method known in the chemical art. For example, suitable
methods are reviewed in Chapter 10 of The Chemistry of Sulfonic Acids,
Esters, and their Derivatives; Patai, S, Rappoport, Z., Eds.; pp.
351-399, John Wiley and Sons: New York, 1991.

[0011]A second class of latent acids consists of compounds according to
formula (II)

R1YSO3-+NHR2R3R4 (II)

wherein Y and R1-R4 are as defined above in relation to formula
(I). Compounds according to formula (II) are ammonium salts of acids, and
dissociation of these salts yields the free amine and the free acid, the
latter of which is active for the purposes of this invention. Methods of
preparing compounds according to formula (II) are well known to those of
ordinary skill in the chemical art.

[0012]A third class of latent acids consists of compounds according to
formula (III)

(R1YSO3)p(OR2)q(NR3R4)rM (III)

wherein Y and R1-R4 are as defined above in relation to formula
(I); M is a Group IVA metal, a Group IVB metal, a Group IB metal, or a
Group IIB metal; and p+q+r=n, where n is the valence of metal M. Any of
R1-R4 may optionally bear an additional oxygen or nitrogen
substituent that bonds to another metal atom, so that dimeric, trimeric,
oligomeric, and polymeric structures containing multiple metal atoms may
also be made for use according to the invention. Nonlimiting examples
include structures according to formula (IIIa),

{(R1YSO3)p(OR2)q-1(NR3R4)rM-OCH.su-
b.2--}2 (IIIa)

which is a dimeric structure belonging to the general class (III) as shown
above. Other examples include compounds according to formula (IIIb)

(R1YSO3)p(OR2)q-2(NR3R4)rM(--OCH.s-
ub.2--CH2O--) (IIIb)

where (--OCH2--CH2O--) represents an ethylene glycol moiety
bonded at both ends to the same metal atom M.

[0013]Latent acids may react in the production zone of the well to form
active acidic species, for example sulfonic acids, mineral acids, etc.
These in turn react with minerals to form water-soluble salts, thus
removing solid minerals to enhance to enhance the porosity of the rock
formation, removing debris from the production zone or wellbore, or
removing acid-labile materials purposely placed in the well to perform
some particular function.

[0014]The latency characteristic of compounds according to formula (I)
refers to their potential for delayed reactivity, thus allowing greater
radial diffusion through the rock formation in the production zone of the
well before formation of the acidic species and their subsequent reaction
with carbonate, silicate, sulfide, or other minerals, which allows
removal of the dissolved minerals from the formation and the wellbore.
Exemplary water-soluble salts produced in this way include, as
nonlimiting examples, calcium, magnesium, barium, and iron salts derived
from methanesulfonic acid and hydrochloric acid, as well as
fluorosilicates derived from hydrofluoric acid and siliceous minerals.
The methanesulfonic (and in some cases, hydrochloric) acid generated by
certain embodiments of this invention, particularly methanesulfonyl
chloride and the various methanesulfonate esters, generally form highly
soluble calcium and magnesium salts. Similarly, hexafluorosilicate salts
of sodium, magnesium, and iron are also soluble. These may be formed, for
example, when the latent acid is a sulfonyl fluoride that contacts silica
deposits containing any of these metals. Latent acids according to
formula (I) typically have relatively low solubility in water or brine
media, and this is believed to contribute to their delayed reaction with
water to form active acids.

[0015]Following are examples of reactions that may occur when the latent
acids come into contact with carbonate-containing rock in the presence of
water. It must be emphasized that these exemplary reactions, and those in
the following sections, may or may not occur exactly as shown. The
precise mechanisms are not critical to the practice of the invention, as
long as dissolution of undesirable particles occurs in a manner
sufficient to improve petroleum flow.

[0016]For removal of calcium carbonate with sulfonyl halides
R1SO2X, where X is chloride, bromide or iodide, the following
may occur:

[0017]Hydrolysis of sulfonyl halides is strongly temperature dependent,
occurring at very slow rates at ambient temperatures, but more rapidly at
elevated temperatures such as may typically be found in the production
zone of an oil well. Also, sulfonyl halide latent acids useful in the
practice of this invention are typically of relatively low solubility in
water at neutral or acidic pH, and this also tends to slow the hydrolysis
of the sulfonyl halide according to Eqn. 1a. Additionally, the pH of the
production zone is typically high due to the presence of carbonates
and/or other basic minerals, and this may accelerate the formation of
active acids in those areas that contain such minerals. Thus, these
dependencies of hydrolysis rate (i.e., Eqn. 1a) on the temperature and
the pH of the medium may both contribute to the latency of acid activity
for compounds of formula (I).

[0018]Once formed, the sulfonic (and hydrohalic, in some cases) acid will
then diffuse through the largely aqueous medium until it contacts solid
carbonate-containing minerals, whereupon the neutralization reactions
(Eqns. 1b and 1 c) may occur to form the water-soluble salt products. In
the absence of other acidic or alkaline species, the degree of conversion
of calcium carbonate to HCO3- or CO2 species shown in
Eqns. 1b and 1c depends on the pH of the aqueous medium, which in turn is
governed by the relative rates of hydrolysis of the sulfonyl halide as
compared to the dissolution and subsequent reaction of the carbonate
species, as well as on the presence of other alkaline species other than
carbonate that may be present.

[0019]Similar chemistry may operate for acid halides of the formula
R1YSO2X. In this case, the R1YSO3- species may
undergo further hydrolysis and neutralizations to form R1YH and
hydrated forms of calcium sulfate.

[0020]In cases where the latent acids are acid fluorides of the formula
R1SO2F or R1YSO2F, one of the hydrolysis products is
HF, which is strongly reactive with silica to form H2SiF6,
which can subsequently react with carbonates or other basic minerals to
form water-soluble hexafluorosilicate salts (not shown).

[0021]In the case where the latent acids are esters of the formulas
R1SO2ZCR2R3R4 and
R1YSO2ZCR2R3R4, the initial hydrolysis reaction
is also strongly temperature dependent. Moreover, the solubilities of
these latent acids in aqueous media decrease markedly with increasing
size of the R1, R2, R3 and R4 groups, thereby
increasing their latency characteristics. Taking the case of the latent
acids of the formula R1SO2OCR2R3R4 (i.e.,
Z═O) as an example, the initial hydrolysis reaction can be
represented as follows, with resulting sulfonic acid R1SO3H
further reacting with the calcium carbonate as previously discussed.

[0022]In the case where the latent acids are esters of the formulas
R1SO2ZCR2R3R4 and
R1YSO2ZCR2R3R4, incorporation of nucleophilic
agents into the formulation may in some embodiments be used to increase
the rate of conversion of the latent acid to an active acid. In the case
of latent acids of the formula R1SO2OCR2R3R4
(i.e., Z═O) as an example, the initial reaction with the nucleophile
(Nu--H) can be represented as follows, with the resulting sulfonic acid
R1SO3H further reacting with the calcium carbonate as
previously discussed.

Other Ingredients

[0023]In order to modify the reactivity and improve the handling
characteristics of the latent acids, it may be desirable to combine them
in a formulation with other materials such as catalysts, solvents, water,
aqueous acids or salts, emulsifying agents, corrosion inhibitors,
viscosity modifiers, etc. Such additives may, for example, alter
reactivity, provide an additional benefit such as corrosion protection,
improved handling characteristics, decreased vapor pressure of
undesirable components, or produce or modify the additive on the surface
prior to injection into the well, in the well, or in the rock formation.
Depending on the solubility characteristics of the latent acid, any
number of organic solvents may also be added. Examples of suitable
solvents for some or all of the above latent acids include diesel fuel,
toluene, xylenes, halogenated solvents, alcohols, ketones, and esters.
The latent acids may also be prepared in the form of an emulsion or
suspension incorporating water, aqueous acids or salts, emulsifying
agents, and optional solvents. Hydrochloric acid, hydrofluoric acid,
sulfamic acid, acetic acid, and formic acid are examples of suitable
aqueous acids.

[0024]In those cases where the latent acid presents worker-exposure or
flammability hazards, it may also be combined with an immiscible liquid
with a density substantially lower than that of the latent acid, such
that the immiscible liquid serves as a barrier to reduce the vapor
pressure of the latent acid. Such barrier materials may include
low-flammability hydrocarbons (e.g., mineral oils), and silicone fluids.
Alternatively, the latent acids may be combined with solid organic or
inorganic adsorbants, so as to allow the controlled release of the latent
acids when these combined materials are suspended in water or other media
for delivery to the targeted strata via the wellbore. Examples of
suitable adsorbants include clays, aluminas, silicas, polyacrylic
acids/amides/esters, polymethacrylic acids/amides/esters, polyamides,
polyesters, polyethers, polyvinyl alcohol, etc., possessing suitable
adsorptive and release properties for the particular latent acid being
employed. The latent acid may be formulated within an encapsulating
material such as wax.

[0026]Nucleophilic agents may optionally be incorporated into these
formulations in super- or sub-stoichiometric amounts to modify the
reactivity of the latent acids, particularly when the latent acids is a
sulfonate ester of the formula R1SO2OCR2R3R4 or
R1YSO2OCR2R3R4 as defined above. In these cases,
the nucleophile may react with the --CR2R3R4 group to
liberate the R1SO3- or R1YSO3- groups in
salt or acid form for reaction with carbonate, silicate, sulfide, or
other minerals. Representative examples of these nucleophilic agents
include, but are not limited to, amines, thiols, alcohols, and
combination thereof, such as triethylamine, triethanolamine,
diethylamine, diethanolamine, dibutylamine, diamylamine, pyridine,
quinolines, lutidine, C1-C30 alkanethiols, dithiols or
polythiols, n-dodecanethiol, t-dodecanethiol, C1-C30 alkanols,
diol, polyols, methanol, isopropanol, ethylene glycol, diethyleneglycol,
triethylene glycol, ethylene glycol monoethers, 2-ethylhexanol, octanol,
fatty alcohols, phenol, and cresols. Typically, thiols or amines will be
used. An extension of the above involves the use of sulfite as the
nucleophile, wherein the resulting products is two sulfonic salts. An
example is the reaction of sodium sulfite with methyl methanesulfonate as
follows.

CH3SO3CH3+NaHSO3→CH3SO3Na+CH3SO.-
sub.3H

[0027]Another embodiment of the invention uses a formulation wherein a
first latent acid reacts with another ingredient to form a second latent
acid in the well or the production zone. One exemplary embodiment uses a
formulation comprising a sulfonyl chloride (the first latent acid), an
alcohol and optionally a catalyst and/or solvent. The alcohol reacts with
the sulfonyl chloride to produce a sulfonate ester (the second latent
acid) and hydrochloric acid (an active acid).

[0028]Another embodiment uses a formulation that comprises a latent acid
that can be oxidized in the wellbore to a sulfonic acid. For example, a
thiolsulfonate may be formulated with an oxidizing agent so that upon
contact with high temperature or a catalyst in the well, a sulfonic acid
is produced. Nonlimiting examples of suitable oxidizers include hydrogen
peroxide, inorganic peroxides, organic peroxides or hydroperoxides,
nitric acid, halogens, and hypohalite salts.

[0029]It should be noted that certain materials, when used in combination
with the latent acids of formula (I), may have a substantial effect on
certain important performance properties of the latent acid. In
particular, materials that might tend to form insoluble products by
reaction with the latent acid (or active acids derived from it) may or
may not be undesirable in a given situation, and therefore some
embodiments of the invention preclude the addition of such compounds in
amounts that produce significant quantities of insoluble products.
Nonlimiting examples of substances that may produce significant
quantities of insoluble products include soluble aluminum compounds,
including but not limited to alkali metal aluminates, and soluble
chromium compounds, including but not limited to CrCl3. These
compounds tend to form insoluble hydroxides, oxides, and/or other
precipitates when contacted with latent acids and/or the active acids
derived from them.

Application of Latent Acids

[0030]The process of this invention involves injection of the latent
acids, optionally within a formulation also comprising catalysts,
solvents, water, aqueous acids or salts, emulsifying agents,
encapsulating agents, vapor-pressure reducing materials, corrosion
inhibitors, viscosity modifiers, and/or other ingredients, into the
wellbore and production zone of the well. Any or all of the various
components of the formulation may be co-injected with the latent acid, or
they may be injected before or after the injection of the latent acid.

[0031]In some embodiments, the composition is injected into strata in the
well having a temperature from 20 to 250° C., typically from 50 to
150° C. In some embodiments, the strata contain predominately
silica-containing rock, and in such cases it may be use for the latent
acid to comprise R1SO2F or R1YSO2F. Alternatively,
the latent acid may comprise R1SO2Cl or R1YSO2Cl, and
it may be accompanied by sodium fluoride, potassium fluoride, or barium
fluoride so that HF is ultimately formed in the strata. HCl and/or HF
themselves may also be added to these or any other formulation containing
a latent acid.

EXAMPLES

Example 1

Methanesulfonyl Chloride as Latent Acid for Reaction with Calcium
Carbonate in Water and in Brine in the Absence of Organic Solvents

[0033]For each tube, the following workup was employed: The tube was
vented of formed CO2 gas and the contents transferred to a syringe
fitted with a filter. The syringe piston was then reattached and the
liquid contents were forced through the filter and collected. The mixed
aqueous and organic filtrates were allowed to separate and the organic
phase removed by pipette. The solids in the filter were then washed with
fresh 1,2-dichloroethane (2.00 g) to remove any absorbed organics and
allowed to combine with the original aqueous phase. The combined aqueous
phase and organic washings were then shaken to extract any residual
sulfonyl chloride in the aqueous phase, and the organic washings combined
with the previously organic phase.

[0034]The combined organic phases for each tube were analyzed by gas
chromatography to determine the amount of unreacted sulfonyl chloride.
The initial amount of sulfonyl chloride in each reaction tube (i.e., time
zero=100% residual sulfonyl chloride) was determined by the gas
chromatographic analysis of a mixture of the sulfonyl chloride (0.12 g)
and the dichloroethane (4.0 g).

[0035]Evaluation of these data reveals that the hydrolysis reaction in
water was largely complete within the first five minutes, while the
hydrolysis rate in brine was substantially suppressed, indicating greater
latency in media with high ionic strength.

Comparative Example 2

Reaction of Calcium Carbonate with Methanesulfonic Acid and with Hydrogen
Chloride

[0036]Methanesulfonic Acid (70%, 0.288 g, 2.10 mmol) was combined with
brine (0.66 g NaCl in 2.00 g water). Calcium carbonate (0.50 g, 5.0 mmol)
was then added and the mixture heated at 80° C. for 30 minutes.
The undissolved solids were then removed by filtration. The experiment
was repeated using an equimolar amount of hydrochloric acid (37%, 0.206
g) in place of the methanesulfonic acid. Examination of both aqueous
filtrates by inductively-coupled plasma spectroscopy revealed each to
contain ca. 16000 ppm (1.6%) Ca2+ content.

Example 3

Methanesulfonyl Chloride in Combination with Solvents as Latent Acids for
Reaction with Calcium Carbonate in the Presence of Organic Solvents

[0038]Evaluation of these data confirm an increase in the amount of
dissolved calcium salts in the reaction mixtures as the hydrolysis of the
sulfonyl chloride proceeded in the presence of either organic solvent.
Moreover, comparison of the levels of residual MSC in the reaction
mixtures 3A and 3B with those reported in 1A revealed slower hydrolysis
rates in the presence of the solvents as compared with the hydrolysis
rates in the absence of the solvents. The data also illustrate the effect
of increasing reaction temperature.

Example 4

Butyl Methanesulfonates as Latent Acids for Reaction with Calcium
Carbonate

[0039]Using the same procedures as described in Example 1 but replacing
the sulfonyl chloride with either n-butyl methanesulfonate (nBMS, 0.15 g)
or sec-butyl methanesulfonate (sBMS, 0.15 g) and only using brine as the
aqueous phase, nine reaction mixtures were prepared, reacted, separated
and analyzed. The results are tabulated below.

[0040]Evaluation of these data reveal a much slower reactivity of these
sulfonate esters in brine media as compared to the sulfonyl chloride
(MSC) in Examples 1 and 3. The greater reactivity and thus poorer latency
of the secondary-alkyl methanesulfonate (sBMS), as compared to the
primary-alkyl methanesulfonate (nBMS), is clearly illustrated in the high
temperature runs.

Example 5

Octyl Methanesulfonates as Latent Acids for Reaction with Calcium
Carbonate in Brine

[0041]Using the same procedures as described in Example 1 but replacing
the sulfonyl chloride with n-octyl methanesulfonate (nOMS, 0.44 g) or
2-ethylhexyl methanesulfonate (EHMS, 0.45 g), using brine as the aqueous
phase, and reducing the CaCO3 charge (0.20 g), four reaction
mixtures were prepared, reacted, separated and analyzed by gas
chromatography to determine residual sulfonate ester. The results are
tabulated below.

[0042]Evaluation of these data reveal even slower reactivity of the nOMS
as compared to the short-chain sulfonate esters described in Example 4.

Example 6

Octyl Methanesulfonates in Combination with Quaternary-Ammonium
Phase-Transfer Catalysts as Latent Acids for Reaction with Calcium
Carbonate

[0043]Reaction mixtures containing n-octyl methanesulfonate (nOMS, 0.44 g)
or 2-ethylhexyl methanesulfonate (EHMS), brine (0.66 g NaCl in 2.00 g
water), calcium carbonate (0.20 g) and a catalytic amount of either
methyl tributylammonium chloride (MTBAC, Cognis ALIQUAT-175) or methyl
tricaprylammonium chloride (MTCAC, Cognis ALIQUAT-336) were prepared,
reacted as discussed Example 3. In these experiments, the amount of
catalyst was 0.01-0.10 mol/mol relative to the sulfonate ester, as
indicated below. After venting off the resulting gas (CO2), the
workup was modified such that 2.00 g of fresh 1,2-dichloroethane
extraction solvent was added to the reaction mixture in each tube. The
contents of the tube was transferred to a syringe fitted with a filter.
The separation and analysis procedures was then continued as in Example
1.

[0044]Comparison of these data with those of Example 5 reveal a
significant catalytic effect of these quaternary alkyl-ammonium chlorides
for the hydrolysis of the sulfonate esters at either 80° C. or
120° C. Comparing the efficacies of the two catalysts, the MTBAC
offered slower reactivity and thus greater latency. For both catalysts,
it was possible to modify the reaction rate by varying the amount of
catalyst.

Example 7

Octyl Methanesulfonate in Combination with Other Surfactants/Catalysts for
Reaction for Reaction with Calcium Carbonate as Latent Acid

[0045]The relative efficacy of nonionic surfactants and anionic
surfactants as catalysts to modify the hydrolysis rates of octyl
methanesulfonate was compared with that for a quaternary alkylammonium
salt (methyl tributylammonium chloride, MTBAC). The tested materials
included PLURONIC non-ionic surfactants (products of BASF) and ARISTONATE
anionic surfactants (products of Pilot Chemical Co.)

[0046]Using the procedures described in Example 6, n-octyl
methanesulfonate (nOMS, 0.44 g) was contacted with calcium carbonate
(0.20 g) in brine (0.66 g NaCl and 2.00 g water) at 80° C. for 120
minutes in the presence of the prospective catalysts (0.44 g). The
results are tabulated below.

[0047]On an equal-weight basis and based on the amount of octanol formed,
the quaternary alkylammonium catalyst provided 8.6-15.2 times the
hydrolysis rate as compared to the non-ionic and anionic surfactants.

[0048]Reaction of phenyl methanesulfonate, water, calcium carbonate and
methyl tributylammonium chloride phase transfer catalyst under the
conditions described in Example 6 revealed no reaction of this aryl
methanesulfonate at reaction temperatures of 80 or 120° C.
Similarly, no reaction was observed for phenyl octanesulfonate with
CaCO3 in saturated brine, or with phenyl methanesulfonate with
aqueous sodium hydroxide in the absence of brine. Thus, aromatic
sulfonate esters are not preferred latent acids for the purposes of this
invention under these particular conditions. However, they may prove
suitable when combined with other catalysts or other additives, and/or at
higher temperatures.

[0049]Although the invention is illustrated and described herein with
reference to specific embodiments, it is not intended that the subjoined
claims be limited to the details shown. Rather, it is expected that
various modifications may be made in these details by those skilled in
the art, which modifications may still be within the spirit and scope of
the claimed subject matter and it is intended that these claims be
construed accordingly.